Technical Field
This disclosure relates to a control unit, an optical deflection system, an image projection apparatus, and a control method.
Background Art
Moveable devices such as an optical deflection device having a reflector are used to deflect a light beam for optical scanning, in which a voltage is applied to a piezoelectric element to deform the piezoelectric element and to move the reflector by the deformed piezoelectric element. A control unit such as a drive unit controls a drive voltage having a given waveform to be applied to the piezoelectric element of the moveable device as disclosed, for example, JP-2015-55829-A. Typically, the control unit sets the drive voltage based on an assumption that the piezoelectric constant value is constant even if the drive voltage values change.
However, actually, the piezoelectric constant value varies depending on the drive voltage values. For example, the piezoelectric constant changes greatly near a minimum value of the drive voltage, in which deformation of the piezoelectric element does not become proportional to the change of drive voltage, and a constantness of a movement speed of the reflector is not achieved.